1. Field of the Invention
The invention relates to the field of crop protection compositions which can be used against harmful plants in tolerant or resistant crops of cereals (such as, for example, common wheat, barley, triticale, rye and oats) and comprise, as herbicidally active compounds, a combination of two or more herbicides.
2. Description of Related Art
The introduction of tolerant or resistant cereal varieties and cereal lines, in particular transgenic cereal varieties, cereal hybrids and cereal lines, adds novel active compounds which per se are not selective in conventional cereal varieties, to the conventional weed control system. The active compounds are, for example, the known broad-spectrum herbicides such as glyphosate, sulfosate, glufosinate, bilanafos (=bialaphos) and imidazolinone herbicides, which can now be employed in the tolerant crops developed specifically for them. The efficacy of these herbicides against harmful plants in the tolerant crops is high, but depends—similarly to other herbicide treatments—on the nature of the herbicide employed, its application rate, the preparation in question, the harmful plants to be controlled, the climatic conditions, the soil conditions etc. Furthermore, the herbicides exhibit weak points (zero effect) against specific species of harmful plants. Another criterion is the duration of action, or the degradation rate of the herbicide. If appropriate, changes in the sensitivity of harmful plants (development of resistance), which may occur upon prolonged use of the herbicides or within a geographical limited area, must also be taken into consideration. The loss of action against individual plants can only be compensated for to a certain extent by higher application rates of the herbicides, if at all. Moreover, there is always a demand for methods to achieve the herbicidal effect with lower application rates of active compounds. A lower application rate not only reduces the amount of an active compound required for application, but as a rule, also reduces the amount of formulation auxiliaries required. Both reduce the economic outlay and improve the eco-friendliness of the herbicide treatment.
One possibility for improving the use profile of a herbicide may consist in combining the active compound with one or more other active compounds which contribute the desired additional properties. However, the combined use of a plurality of active compounds does not infrequently lead to phenomena of a physical and biological incompatibility, for example lacking stability of a coformulation, decomposition of an active compound or antagonism in the biological action of the active compounds. In contrast, what is desired are combinations of active compounds with a favorable profile of action, high stability and, ideally, synergistically enhanced activity, which allows the application rate to be reduced in comparison with the individual application of the active compounds to be combined.
Compounds (A) and (B) are known. Compounds of type (A1) are described, for example, in DE-A 2717440. Compounds of type (B1) are described, for example, in WO 2007/082098. Mixtures of these compounds with other herbicides are described, for example, in WO 2009/029518. This publication also describes synergistic mixtures of some of the (B)-components according to the invention with the total herbicide glyphosate, but not their use in tolerant crops, but only synergism with respect to the herbicidal action against weed grasses/broad-leaved weeds.
WO 2007/120706 A2 describes synergistic herbicide combinations (01, p. 1, lines 8-11) comprising a pyrimidinecarboxylic acid of the formula I (see p. 2, lines 6-16) and a second herbicide (for example a GS (glutamine synthase) inhibitor (01, p. 2, line 25)) or herbicide safener.
US-A-2002/094934 describes herbicide combinations comprising a herbicide A (see p. 1, A. 6-14) and a herbicide B (see pp. 1-2, A. 15-19).
US-A-2007/179059 describes pyrimidinecarboxylic acids and their derivatives of the formula I (see 04, pp. 1-2).
Surprisingly, it has now been found that certain active compounds from the class of the abovementioned broad-spectrum herbicides (A) in combination with certain herbicides (B) interact in a particularly favorably (synergistic) manner when they are employed in the cereal crops which are suitable for the selective use of the first-mentioned herbicides.